Hybrid GozNym malware targets customers of 24 financial institutions

A group of cybercriminals have combined two powerful malware programs to create a new online banking Trojan that has already stolen millions of dollars from customers of 24 US and Canadian banks.

The new threat has been dubbed GozNym by researchers from IBM X-Force because it combines the stealthy Nymaim malware and the Gozi banking Trojan.

The new computer Trojan targets 22 websites that belong to banks, credit unions and e-commerce platforms based in the US, and two that belong to financial institutions from Canada. Business banking services appear to be a top target for GozNym's creators, according to the IBM researchers.

Nymaim is what researchers call a dropper. Its purpose is to download and run other malware programs on infected computers. It is usually distributed through Web-based exploits launched from compromised websites.

Nymaim uses detection evasion techniques such as encryption, anti-VM and anti-debugging routines, and control flow obfuscation. In the past, it has primarily been used to install ransomware on computers.

However, since November, the cybercriminal gang that controls Nymaim has switched to banking fraud. Specifically, the dropper started loading a DLL that is part of the Gozi ISFB malware and which is capable of injecting malicious code into Web browsing sessions. This technique is most frequently used to perform online banking fraud.

The integration between Nymaim and Gozi became complete in April, when a new version was discovered that combined code from both threats in a single new Trojan - GozNym.

"This malware is as stealthy and persistent as the Nymaim loader while possessing the Gozi ISFB Trojan’s ability to manipulate Web sessions, resulting in advanced online banking fraud attacks," the IBM X-Force researchers said in a blog post.

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